Therapeutic agents delivered in a conventional or non-specific manner, such as by oral dosing or intravenous administration, are often distributed to non-designated areas of the body. As a consequence, the agent may be metabolized, for example, through first pass metabolism of the liver, thereby resulting in diminished bioavailability and the possibility for increased dosing at a higher cost and with the risk of adverse side effects. In addition, non-specific distribution of therapeutic agents may result in adverse effects and unwanted pharmacological responses in the subject to which they are administered. As a result, certain agents may be contraindicated in certain subjects or under certain conditions.
Nanoparticles and microparticles have shown potential as vehicles for the targeted delivery of therapeutic agents, including enzymes for enzyme replacement therapy, hormones, cell modifying agents and genetic material. Attempts to use nanoparticles and microparticles for site-specific delivery have shown potential to lower adverse effects in patients, attributed in part to lower doses of therapeutic agents being required. However, there is a significant unmet medical need for site-specific drug delivery, for example in injured arteries after angioplasty and stenting, that inhibits redistribution of the drug and allows for greater retention of the drug at the injured site.